That's what New Zealand outdoors entrepreneur Guy Howard-Willis wondered back in 2010, when he conceived of the Manta5. In the years since, bicycle designer Roland Alonzo brought the concept to life, in the form of an electric-assist pedal-powered hydrofoil bike. Now, it's just about ready to enter the market.
The Manta5 has an aluminum frame, two carbon fiber hydrofoils that provide lift, and a 400-watt motor that augments the rider's pedalling power to turn the propeller. Although it has no actual hull, it does have buoyancy modules that keep it afloat when stopped. Additionally, unlike the case with some hobbyist hydrofoil bikes, it's possible to get back on and get it planing again, if you should dismount while out on the water.
The whole thing weighs around 20 kg (44 lb), and can be partially disassembled for transport in the back of a car. It's designed for riders weighing between 70 and 100 kg (154 and 220 lb), and can be used in both fresh and salt water.
As with land-going e-bikes, riders can adjust the amount of electrical assistance provided, depending on how hard they want to work. The current prototype version can run for an average of about one hour per charge of its removable battery, and reach a top speed of 15 to 20 km/h (9 to 12 mph). Plans call for the first limited-edition production model – the Hydrofoiler XE-1, pictured below – to be faster.